1. n. [Geology]

The approximate age determination of rocks, fossils or minerals made by comparing whether the material is younger or older than other surrounding material. Relative age is estimated according to stratigraphic and structural relationships, such as superposition, and by fossil content, since the relative ages and successions of fossils have been established by paleontologists. The measurement of the decay of radioactive isotopes, especially uranium, rubidium, argon and carbon, has allowed geologists to more precisely determine the age in years of rock formations, known as the absolute age. Tree rings and seasonal sedimentary deposits called varves can be counted to determine absolute age. Although the term implies otherwise, "absolute" ages typically have some amount of potential error and are inexact.

See related terms: absolute age,  chronostratigraphy,  formation,  geochronology,  geologic time scale,  lithologic contact,  paleontology,  plankton,  stratigraphy,  superposition,  varve